1. Field of the Invention
The present invention relates generally to valves for controlling the intermittent flooding or flushing of liquids into a vessel, and more particularly to apparatus for controlling the circulation of hydroponic solutions to and from cultivation containers for plants.
In hydroponic culture, a common mode of operation is termed “ebb and flow”. In this operation, plants are contained in a culture vessel and the roots are intermittently flooded with a nutrient solution, and then the solution is allowed to drain out. It is important that this “ebb and flow” operation be automated and functions reliably. If the plants roots are not flooded in time, they will dry out resulting in irreparable damage to the plant roots. On the other hand if the hydroponic solution stagnates in the cultivation container, then the roots will rot, again causing irrecoverable damage. In addition to reliable operation, it is essential that the device be low cost and preferably not require a power source.
2. Statement of the Prior Art
In the prior art, the vast majority of such “ebb and flow” valves use a float mechanism. In these devices, a float assembly moves as the water level rises in the plant cultivation vessel. When the liquid level is at the desired height, the float shuts the feed valve off and liquid drains out of the cultivation container back into the feed reservoir. In most cases a low pressure pump is required to provide the feed solution. The biggest problem with float valves is that they have mechanical moving parts and these parts tend to get clogged by roots and other foreign matter that prevent the float from moving freely. The float valves also have small diameter seats in order to make them compact. These limitations cause float valves to frequently malfunction, leading to catastrophic crop failure. Pinch valves have been used as an alternative, but these require a power source to open and close the valve. This results in increased complexity and cost. While pinch valves are less prone to clogging, the possible failure of the power source reduces overall reliability. Other prior art approaches eliminate a valve altogether by having a bleeder orifice or venturi. These require high pressure pumps in order to generate sufficient flow to the cultivation vessel and also suffer from the problem that the drain orifice is usually very small and easily clogged, leading to stagnant hydroponic solution remaining in contact with the plant roots and possible root rot.